package lobby

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"slices"
	"time"

	"github.com/go-jet/jet/v2/postgres"
	"github.com/go-jet/jet/v2/qrm"
	"github.com/google/uuid"

	"scrabble/backend/internal/account"
	"scrabble/backend/internal/engine"
	"scrabble/backend/internal/game"
	"scrabble/backend/internal/postgres/jet/backend/model"
	"scrabble/backend/internal/postgres/jet/backend/table"
)

// invitationTTL is how long an unanswered invitation stays open before it lazily
// expires.
const invitationTTL = 7 * 24 * time.Hour

// Invitation statuses.
const (
	invitationPending   = "pending"
	invitationDeclined  = "declined"
	invitationCancelled = "cancelled"
	invitationExpired   = "expired"
	invitationStarted   = "started"
)

// Invitee responses.
const (
	inviteePending  = "pending"
	inviteeAccepted = "accepted"
	inviteeDeclined = "declined"
)

// InvitationSettings are the game settings an inviter chooses. A zero TurnTimeout
// defaults to game.DefaultTurnTimeout; the zero DropoutTiles removes a leaver's
// tiles from play.
type InvitationSettings struct {
	Variant        engine.Variant
	TurnTimeout    time.Duration
	HintsAllowed   bool
	HintsPerPlayer int
	DropoutTiles   engine.DropoutTiles
}

// Invitee is one invited player's seat and response.
type Invitee struct {
	AccountID uuid.UUID
	Seat      int
	Response  string
}

// Invitation is a friend-game invitation with its invitees.
type Invitation struct {
	ID        uuid.UUID
	InviterID uuid.UUID
	Settings  InvitationSettings
	Status    string
	GameID    *uuid.UUID
	ExpiresAt time.Time
	CreatedAt time.Time
	Invitees  []Invitee
}

// InvitationService creates and resolves friend-game invitations, starting the
// game through a GameCreator once every invitee has accepted.
type InvitationService struct {
	store    *Store
	games    GameCreator
	accounts *account.Store
	blocker  Blocker
	now      func() time.Time
}

// NewInvitationService constructs an InvitationService. store owns the invitation
// tables; games starts the accepted game; accounts validates invitees; blocker
// refuses invitations across a block.
func NewInvitationService(store *Store, games GameCreator, accounts *account.Store, blocker Blocker) *InvitationService {
	return &InvitationService{
		store:    store,
		games:    games,
		accounts: accounts,
		blocker:  blocker,
		now:      func() time.Time { return time.Now().UTC() },
	}
}

// CreateInvitation records a pending invitation from inviterID to inviteeIDs (in
// seat order, 1..N) with the given settings. The total seat count must be 2-4,
// invitees distinct and not the inviter, every invitee an existing account with no
// block standing between them, and the settings acceptable.
func (svc *InvitationService) CreateInvitation(ctx context.Context, inviterID uuid.UUID, inviteeIDs []uuid.UUID, settings InvitationSettings) (Invitation, error) {
	if n := len(inviteeIDs) + 1; n < 2 || n > 4 {
		return Invitation{}, fmt.Errorf("%w: need 2-4 players, got %d", ErrInvalidInvitation, n)
	}
	if settings.HintsPerPlayer < 0 {
		return Invitation{}, fmt.Errorf("%w: hints per player must be >= 0", ErrInvalidInvitation)
	}
	if settings.TurnTimeout == 0 {
		settings.TurnTimeout = game.DefaultTurnTimeout
	}
	if !slices.Contains(game.AllowedTurnTimeouts, settings.TurnTimeout) {
		return Invitation{}, fmt.Errorf("%w: turn timeout %s not allowed", ErrInvalidInvitation, settings.TurnTimeout)
	}
	seen := map[uuid.UUID]bool{inviterID: true}
	for _, id := range inviteeIDs {
		if seen[id] {
			return Invitation{}, fmt.Errorf("%w: %s invited twice or is the inviter", ErrInvalidInvitation, id)
		}
		seen[id] = true
		if _, err := svc.accounts.GetByID(ctx, id); err != nil {
			if errors.Is(err, account.ErrNotFound) {
				return Invitation{}, fmt.Errorf("%w: invitee %s not found", ErrInvalidInvitation, id)
			}
			return Invitation{}, err
		}
		blocked, err := svc.blocker.IsBlocked(ctx, inviterID, id)
		if err != nil {
			return Invitation{}, err
		}
		if blocked {
			return Invitation{}, ErrInvitationBlocked
		}
	}

	id, err := uuid.NewV7()
	if err != nil {
		return Invitation{}, fmt.Errorf("lobby: new invitation id: %w", err)
	}
	ins := invitationInsert{
		id:              id,
		inviterID:       inviterID,
		variant:         settings.Variant.String(),
		turnTimeoutSecs: int(settings.TurnTimeout / time.Second),
		hintsAllowed:    settings.HintsAllowed,
		hintsPerPlayer:  settings.HintsPerPlayer,
		dropoutTiles:    settings.DropoutTiles.String(),
		expiresAt:       svc.now().Add(invitationTTL),
	}
	if err := svc.store.insertInvitation(ctx, ins, inviteeIDs); err != nil {
		return Invitation{}, err
	}
	return svc.store.loadInvitation(ctx, id)
}

// RespondInvitation records accountID's accept or decline of an invitation. A
// decline cancels the whole invitation; the accept that completes the set starts
// the game and marks the invitation started.
func (svc *InvitationService) RespondInvitation(ctx context.Context, invitationID, accountID uuid.UUID, accept bool) (Invitation, error) {
	res, err := svc.store.respondTx(ctx, invitationID, accountID, accept, svc.now())
	if err != nil {
		return Invitation{}, err
	}
	if accept && res.allAccepted {
		if err := svc.startGame(ctx, invitationID); err != nil {
			return Invitation{}, err
		}
	}
	return svc.store.loadInvitation(ctx, invitationID)
}

// startGame creates the game for a fully-accepted invitation and marks it started.
func (svc *InvitationService) startGame(ctx context.Context, invitationID uuid.UUID) error {
	inv, err := svc.store.loadInvitation(ctx, invitationID)
	if err != nil {
		return err
	}
	seats := make([]uuid.UUID, len(inv.Invitees)+1)
	seats[0] = inv.InviterID
	for _, iv := range inv.Invitees {
		if iv.Seat < 1 || iv.Seat >= len(seats) {
			return fmt.Errorf("lobby: invitation %s has out-of-range seat %d", invitationID, iv.Seat)
		}
		seats[iv.Seat] = iv.AccountID
	}
	g, err := svc.games.Create(ctx, game.CreateParams{
		Variant:        inv.Settings.Variant,
		Seats:          seats,
		TurnTimeout:    inv.Settings.TurnTimeout,
		HintsAllowed:   inv.Settings.HintsAllowed,
		HintsPerPlayer: inv.Settings.HintsPerPlayer,
		DropoutTiles:   inv.Settings.DropoutTiles,
	})
	if err != nil {
		return err
	}
	if _, err := svc.store.markStarted(ctx, invitationID, g.ID, svc.now()); err != nil {
		return err
	}
	return nil
}

// CancelInvitation lets the inviter withdraw a pending invitation.
func (svc *InvitationService) CancelInvitation(ctx context.Context, invitationID, inviterID uuid.UUID) error {
	return svc.store.cancelInvitation(ctx, invitationID, inviterID, svc.now())
}

// GetInvitation loads an invitation with its invitees.
func (svc *InvitationService) GetInvitation(ctx context.Context, invitationID uuid.UUID) (Invitation, error) {
	return svc.store.loadInvitation(ctx, invitationID)
}

// invitationInsert carries the immutable fields of a new invitation.
type invitationInsert struct {
	id              uuid.UUID
	inviterID       uuid.UUID
	variant         string
	turnTimeoutSecs int
	hintsAllowed    bool
	hintsPerPlayer  int
	dropoutTiles    string
	expiresAt       time.Time
}

// respondResult reports the state after an invitee response.
type respondResult struct {
	allAccepted bool
}

// insertInvitation inserts the invitation and one invitee row per id (seats 1..N).
func (s *Store) insertInvitation(ctx context.Context, ins invitationInsert, inviteeIDs []uuid.UUID) error {
	return withTx(ctx, s.db, func(tx *sql.Tx) error {
		ii := table.GameInvitations.INSERT(
			table.GameInvitations.InvitationID, table.GameInvitations.InviterID, table.GameInvitations.Variant,
			table.GameInvitations.TurnTimeoutSecs, table.GameInvitations.HintsAllowed, table.GameInvitations.HintsPerPlayer,
			table.GameInvitations.DropoutTiles, table.GameInvitations.ExpiresAt,
		).VALUES(ins.id, ins.inviterID, ins.variant, ins.turnTimeoutSecs, ins.hintsAllowed, ins.hintsPerPlayer, ins.dropoutTiles, ins.expiresAt)
		if _, err := ii.ExecContext(ctx, tx); err != nil {
			return fmt.Errorf("insert invitation: %w", err)
		}
		for i, id := range inviteeIDs {
			pi := table.GameInvitationInvitees.INSERT(
				table.GameInvitationInvitees.InvitationID, table.GameInvitationInvitees.AccountID, table.GameInvitationInvitees.Seat,
			).VALUES(ins.id, id, i+1)
			if _, err := pi.ExecContext(ctx, tx); err != nil {
				return fmt.Errorf("insert invitee %d: %w", i+1, err)
			}
		}
		return nil
	})
}

// loadInvitation reads an invitation and its invitees ordered by seat.
func (s *Store) loadInvitation(ctx context.Context, id uuid.UUID) (Invitation, error) {
	isel := postgres.SELECT(table.GameInvitations.AllColumns).
		FROM(table.GameInvitations).
		WHERE(table.GameInvitations.InvitationID.EQ(postgres.UUID(id))).
		LIMIT(1)
	var row model.GameInvitations
	if err := isel.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Invitation{}, ErrInvitationNotFound
		}
		return Invitation{}, fmt.Errorf("lobby: load invitation %s: %w", id, err)
	}
	variant, err := engine.ParseVariant(row.Variant)
	if err != nil {
		return Invitation{}, fmt.Errorf("lobby: invitation %s: %w", id, err)
	}
	dropout, err := engine.ParseDropoutTiles(row.DropoutTiles)
	if err != nil {
		return Invitation{}, fmt.Errorf("lobby: invitation %s: %w", id, err)
	}
	inv := Invitation{
		ID:        row.InvitationID,
		InviterID: row.InviterID,
		Settings: InvitationSettings{
			Variant:        variant,
			TurnTimeout:    time.Duration(row.TurnTimeoutSecs) * time.Second,
			HintsAllowed:   row.HintsAllowed,
			HintsPerPlayer: int(row.HintsPerPlayer),
			DropoutTiles:   dropout,
		},
		Status:    row.Status,
		GameID:    row.GameID,
		ExpiresAt: row.ExpiresAt,
		CreatedAt: row.CreatedAt,
	}
	psel := postgres.SELECT(table.GameInvitationInvitees.AllColumns).
		FROM(table.GameInvitationInvitees).
		WHERE(table.GameInvitationInvitees.InvitationID.EQ(postgres.UUID(id))).
		ORDER_BY(table.GameInvitationInvitees.Seat.ASC())
	var prows []model.GameInvitationInvitees
	if err := psel.QueryContext(ctx, s.db, &prows); err != nil {
		return Invitation{}, fmt.Errorf("lobby: load invitees %s: %w", id, err)
	}
	for _, p := range prows {
		inv.Invitees = append(inv.Invitees, Invitee{AccountID: p.AccountID, Seat: int(p.Seat), Response: p.Response})
	}
	return inv, nil
}

// respondTx applies an invitee's response inside a row-locked transaction so
// concurrent responses serialise and exactly one accept can complete the set.
func (s *Store) respondTx(ctx context.Context, invitationID, accountID uuid.UUID, accept bool, now time.Time) (respondResult, error) {
	var res respondResult
	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
		isel := postgres.SELECT(table.GameInvitations.Status, table.GameInvitations.ExpiresAt).
			FROM(table.GameInvitations).
			WHERE(table.GameInvitations.InvitationID.EQ(postgres.UUID(invitationID))).
			FOR(postgres.UPDATE())
		var inv model.GameInvitations
		if err := isel.QueryContext(ctx, tx, &inv); err != nil {
			if errors.Is(err, qrm.ErrNoRows) {
				return ErrInvitationNotFound
			}
			return fmt.Errorf("lock invitation: %w", err)
		}
		if inv.Status == invitationPending && now.After(inv.ExpiresAt) {
			if err := setInvitationStatus(ctx, tx, invitationID, invitationExpired, now); err != nil {
				return err
			}
			return ErrInvitationExpired
		}
		if inv.Status != invitationPending {
			return ErrInvitationNotPending
		}

		psel := postgres.SELECT(table.GameInvitationInvitees.Response).
			FROM(table.GameInvitationInvitees).
			WHERE(
				table.GameInvitationInvitees.InvitationID.EQ(postgres.UUID(invitationID)).
					AND(table.GameInvitationInvitees.AccountID.EQ(postgres.UUID(accountID))),
			).LIMIT(1)
		var invitee model.GameInvitationInvitees
		if err := psel.QueryContext(ctx, tx, &invitee); err != nil {
			if errors.Is(err, qrm.ErrNoRows) {
				return ErrNotInvited
			}
			return fmt.Errorf("load invitee: %w", err)
		}
		if invitee.Response != inviteePending {
			return ErrAlreadyResponded
		}

		if !accept {
			if err := setInviteeResponse(ctx, tx, invitationID, accountID, inviteeDeclined, now); err != nil {
				return err
			}
			return setInvitationStatus(ctx, tx, invitationID, invitationDeclined, now)
		}

		if err := setInviteeResponse(ctx, tx, invitationID, accountID, inviteeAccepted, now); err != nil {
			return err
		}
		remaining, err := unacceptedInvitees(ctx, tx, invitationID)
		if err != nil {
			return err
		}
		res.allAccepted = remaining == 0
		return nil
	})
	return res, err
}

// markStarted stamps a fully-accepted invitation as started, only while it is
// still pending, and reports whether it did.
func (s *Store) markStarted(ctx context.Context, invitationID, gameID uuid.UUID, now time.Time) (bool, error) {
	stmt := table.GameInvitations.
		UPDATE(table.GameInvitations.Status, table.GameInvitations.GameID, table.GameInvitations.UpdatedAt).
		SET(postgres.String(invitationStarted), postgres.UUID(gameID), postgres.TimestampzT(now)).
		WHERE(
			table.GameInvitations.InvitationID.EQ(postgres.UUID(invitationID)).
				AND(table.GameInvitations.Status.EQ(postgres.String(invitationPending))),
		)
	res, err := stmt.ExecContext(ctx, s.db)
	if err != nil {
		return false, fmt.Errorf("lobby: mark started: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return false, fmt.Errorf("lobby: mark started rows: %w", err)
	}
	return n > 0, nil
}

// cancelInvitation withdraws a pending invitation on behalf of its inviter.
func (s *Store) cancelInvitation(ctx context.Context, invitationID, inviterID uuid.UUID, now time.Time) error {
	stmt := table.GameInvitations.
		UPDATE(table.GameInvitations.Status, table.GameInvitations.UpdatedAt).
		SET(postgres.String(invitationCancelled), postgres.TimestampzT(now)).
		WHERE(
			table.GameInvitations.InvitationID.EQ(postgres.UUID(invitationID)).
				AND(table.GameInvitations.InviterID.EQ(postgres.UUID(inviterID))).
				AND(table.GameInvitations.Status.EQ(postgres.String(invitationPending))),
		)
	res, err := stmt.ExecContext(ctx, s.db)
	if err != nil {
		return fmt.Errorf("lobby: cancel invitation: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("lobby: cancel invitation rows: %w", err)
	}
	if n == 0 {
		// Either the invitation is gone, not the caller's, or no longer pending.
		inv, err := s.loadInvitation(ctx, invitationID)
		if err != nil {
			return err
		}
		if inv.InviterID != inviterID {
			return ErrNotInviter
		}
		return ErrInvitationNotPending
	}
	return nil
}

// unacceptedInvitees counts the invitees of an invitation not yet accepted.
func unacceptedInvitees(ctx context.Context, tx *sql.Tx, invitationID uuid.UUID) (int, error) {
	stmt := postgres.SELECT(table.GameInvitationInvitees.Response).
		FROM(table.GameInvitationInvitees).
		WHERE(table.GameInvitationInvitees.InvitationID.EQ(postgres.UUID(invitationID)))
	var rows []model.GameInvitationInvitees
	if err := stmt.QueryContext(ctx, tx, &rows); err != nil {
		return 0, fmt.Errorf("count invitees: %w", err)
	}
	remaining := 0
	for _, r := range rows {
		if r.Response != inviteeAccepted {
			remaining++
		}
	}
	return remaining, nil
}

// setInvitationStatus updates an invitation's status and updated_at.
func setInvitationStatus(ctx context.Context, tx *sql.Tx, invitationID uuid.UUID, status string, now time.Time) error {
	stmt := table.GameInvitations.
		UPDATE(table.GameInvitations.Status, table.GameInvitations.UpdatedAt).
		SET(postgres.String(status), postgres.TimestampzT(now)).
		WHERE(table.GameInvitations.InvitationID.EQ(postgres.UUID(invitationID)))
	if _, err := stmt.ExecContext(ctx, tx); err != nil {
		return fmt.Errorf("set invitation status: %w", err)
	}
	return nil
}

// setInviteeResponse updates one invitee's response and responded_at.
func setInviteeResponse(ctx context.Context, tx *sql.Tx, invitationID, accountID uuid.UUID, response string, now time.Time) error {
	stmt := table.GameInvitationInvitees.
		UPDATE(table.GameInvitationInvitees.Response, table.GameInvitationInvitees.RespondedAt).
		SET(postgres.String(response), postgres.TimestampzT(now)).
		WHERE(
			table.GameInvitationInvitees.InvitationID.EQ(postgres.UUID(invitationID)).
				AND(table.GameInvitationInvitees.AccountID.EQ(postgres.UUID(accountID))),
		)
	if _, err := stmt.ExecContext(ctx, tx); err != nil {
		return fmt.Errorf("set invitee response: %w", err)
	}
	return nil
}